1. Scatterometer Wind Forcing of an Eddy-Resolving North Atlantic Model Matthew Hecht (Los Alamos) Bill Large (NCAR) Patrice Klein (IFREMER)

2. Wind Stress, Oceanic Kinetic Energy and Inertial Resonance Wind stress depends weakly on u ocn –   (u atm - u ocn ) Kinetic Energy input to ocean can depend strongly on u ocn –  KE = ∫ (  · u ocn ) dt The ocean responds to strong wind forcing by setting up inertial currents, changing direction with frequency f. If –If the ocean model is eddy resolving and the wind forcing includes inertial frequencies then we may see inertial resonance, where  KE is large because  and u ocn rotate together

4. Observed deepening of mixed layer (top) not captured by non-eddy-resolving ocean (bottom) 50ºS

5. Forcing of Eddy-Resolving North Atlantic Ocean Model, with Daily and 12-hourly QSCAT Winds 1/10º POP (Los Alamos’ Parallel Ocean Program) Ocean of Smith et al. (JPO 2000), but with –KPP vertical mixing, 1/2x horz viscosity and diffusivity 2 branch runs, from ECMWF daily wind forced case, using QSCAT/NCEP blended winds –Daily winds (inertial frequencies absent) –12-hourly winds (preserves significant fraction of inertial frequency range) –Concentration on one extreme event, January 21, 2002 Winds produced by Ralph Milliff and Jan Morzel at Colorado Research Associates (CoRA) http://www.colorado-research.com/~morzel/blendedwinds.qscat.dirth.2002.html

7. Histograms of work done by wind on ocean over 3 hour diagnostic periods, daily vs. 12-hourly-forced cases daily 12-hourly Work Log(# grid cells) January, 2002 Work is ∫ (  · u ocn ) dt 0 40002000 -2000 10 6 10 4 10 2

8. Work done by Wind Stress -- January 21, 2002 daily 12-hourly

9. Small Scales in Ocean, Larger Scales in Wind QSCAT Stress  64 dynes/ cm^2! Vorticity January 21, 2002

10. Conclusions Mean input of kinetic energy O.K. with daily winds –Direct influence of higher wind frequencies on linear dynamics is minimal Need eddy-resolving ocean and high- frequency winds (higher than daily) to resolve extreme events –Could have a major impact on non-linear mixing

11. Continuing Work What’s the impact of resolving these extreme, inertial-frequency events? How much impact is there when higher frequency reanalysis winds are used? –“Extreme” events will be less extreme, but… –Can compare daily to 6-hourly